Graphite oxide is a class of an intercalated layered material that is prepared by oxidizing a graphite with an oxidizing agent such as, for example, a chlorate salt or a permanganate salt. Graphite oxides are especially useful as intermediates in the preparation of exfoliated graphites, including graphene. One method of preparing an exfoliated graphite is rapidly heating a graphite oxide to high temperatures as exemplified later herein.
Exfoliated graphite, also known as expanded graphite, generally is an exfoliated or partially delaminated graphite having a Brunauer-Emmett-Teller (BET) surface area greater than BET surface area of graphite but less than the BET theoretical surface area of a single graphene sheet (i.e., less than 2630 square meters per gram (m2/g)). Conventional exfoliated graphite typically has a BET surface area of between about 15 m2/g to about 150 m2/g, depending on average particle size. Exfoliated graphite is useful for a variety of applications including, for example, in the formation of composites such as polymer composites and the higher the BET surface area of the exfoliated graphite, the more useful it is in such composites.
One disadvantage of long-known chlorate salt-based graphite oxidation reaction processes is generation of hazardous chlorine dioxide (ClO2) gas, which is believed to be associated with effective oxidation of the graphite to graphite oxide. But during the reaction, concentration of the ClO2 gas often builds up in headspace of reaction vessels to explosive concentrations (i.e., 10% or higher, for example, 50%). To minimize such hazards, temperature of reaction mixtures in such processes is typically kept at about 0 degrees Celsius (° C.) to 5° C., but this temperature reduces solubility and reactivity of the chlorate salt and can also increase concentration of the chlorine dioxide gas in the headspace of the reaction vessel when the reaction mixtures are warmed or allowed to warm to a higher temperature (typically ambient, i.e., about 25° C.), after addition of the chlorate salt. There is a need in the art for a graphite oxidation process that eliminates this hazard without reducing quality of graphite oxide produced thereby.